The Immunopathology Core will provide direct and indirect support to the various Program Project (PP) investigators and cores in their analyses of malignant, atypical and benign breast lesions. The direct support includes 1) performance of immunohistochemical assays on human tissues and cell lines, 2) microscopic interpretation of these stained tissues and/or cells, 3) generation of data which reflects the immunohistochemical reactivity of specific histologic lesions, 4) entry of these data into the PP database using a personal computer (P[unreadable]) with direct access to the PP via the Internet system, and 5) a retrospective tissue bank of breast carcinomas (n>300) which were surgically excised at the Massachusetts General Hospital (MGH) prior to 1983, with epidemiologic, clinical and follow-up data. These tissues can be analyzed immunohistochemically using specific antibody probes to determine clinical, histologic or prognostic correlations with antigenic expression. Indirect support includes 1) identification of antigens of potential biologic and/or prognostic interest, either reported in the literature or identified by Dr. Thor's laboratory, 2) reevaluation of histopathologic lesions in tissue samples providing histologic confirmation and additional expertise in breast pathology and 3) development of antigen specific biologic questions which are based on the distribution or pattern of cellular expression in breast tissues. Analyses of specific antigens (such as protooncogene products, markers of cellular proliferation, etc.) in breast carcinomas using immunohistochemical techniques can provide rapid, inexpensive and important phenotypic information at the cellular level. Frozen and fixed paraffin- embedded malignant and benign breast tissues collected by the Program Project and the Immunopathology Core are a valuable scientific resource. These tissues will allow the Immunopathology Core to retrospectively and prospectively evaluate the significance of antigen expression in specific breast lesions. Our major goal is to facilitate a correlation between the classically described parameters of breast cancer and phenotypic, biologic or genetic variables investigated by the Program Project in order to identify or define prognostic indicators.